[ASTMangler] Fix USR generation/mangling crash in invalid code

In invalid code a decl may end up with an opened archetype type that the
mangler doesn't expect. We still want to be able to generate a USR for these
decls so that we can index and rename their occurences successfully. To allow
this, this patch calls mapTypeOutOfContext on primary or opened archetype types
prior to mangling.

Resolves rdar://problem/54310026

Author: Nathan Hawes

lib/AST/ASTMangler.cpp

@@ -2356,29 +2356,34 @@ CanType ASTMangler::getDeclTypeForMangling(
   }
 
 
-  CanType type = decl->getInterfaceType()
-                      ->getReferenceStorageReferent()
-                      ->getCanonicalType();
-  if (auto gft = dyn_cast<GenericFunctionType>(type)) {
+  Type type = decl->getInterfaceType()
+                  ->getReferenceStorageReferent();
+  if (type->hasArchetype()) {
+    assert(isa<ParamDecl>(decl) && "Only ParamDecl's still have archetypes");
+    type = type->mapTypeOutOfContext();
+  }
+  CanType canTy = type->getCanonicalType();
+
+  if (auto gft = dyn_cast<GenericFunctionType>(canTy)) {
     genericSig = gft.getGenericSignature();
     CurGenericSignature = gft.getGenericSignature();
 
-    type = CanFunctionType::get(gft.getParams(), gft.getResult(),
-                                gft->getExtInfo());
+    canTy = CanFunctionType::get(gft.getParams(), gft.getResult(),
+                                 gft->getExtInfo());
   }
 
-  if (!type->hasError()) {
+  if (!canTy->hasError()) {
     // Shed the 'self' type and generic requirements from method manglings.
     if (isMethodDecl(decl)) {
       // Drop the Self argument clause from the type.
-      type = cast<AnyFunctionType>(type).getResult();
+      canTy = cast<AnyFunctionType>(canTy).getResult();
     }
 
     if (isMethodDecl(decl) || isa<SubscriptDecl>(decl))
       parentGenericSig = decl->getDeclContext()->getGenericSignatureOfContext();
   }
 
-  return type;
+  return canTy;
 }
 
 void ASTMangler::appendDeclType(const ValueDecl *decl, bool isFunctionMangling) {

test/Index/invalid_code.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-ide-test -print-indexed-symbols -source-filename %s | %FileCheck %s
+// RUN: %target-swift-ide-test -print-indexed-symbols -include-locals -source-filename %s | %FileCheck %s
 
 // CHECK: [[@LINE+1]]:8 | struct/Swift | Int | {{.*}} | Ref | rel: 0
 var _: Int { get { return 1 } }
@@ -37,3 +37,15 @@ public struct BadCollection: Collection {
     public func index(after index: Index) -> Index { }
     public subscript(position: Index) -> Element { }
 }
+
+struct Protector<T> {}
+extension Protector where T: RangeReplaceableCollection {
+  func append(_ newElement: T.Iterator.Element) {
+    undefined { (foo: T) in
+    // CHECK: [[@LINE-1]]:18 | param(local)/Swift | foo | {{.*}} | Def,RelChild
+    // CHECK: [[@LINE-2]]:18 | function/acc-get(local)/Swift | getter:foo | {{.*}} | Def,Impl,RelChild,RelAcc
+    // CHECK: [[@LINE-3]]:18 | function/acc-set(local)/Swift | setter:foo | {{.*}} | Def,Impl,RelChild,RelAcc
+      _ = newElement
+    }
+  }
+}